Development container patterns in Docker - Commands & Configuration

Introduction

Development container patterns help you create isolated environments for coding. They solve the problem of different tools or libraries conflicting on your computer by packaging everything your app needs inside a container.

When you want to ensure your app runs the same way on any computer without setup issues

When you need to share your development environment with teammates easily

When you want to test your app with different versions of tools without changing your main system

When you want to keep your computer clean from many installed dependencies

When you want to quickly start coding without spending time installing software

Config File - Dockerfile

Dockerfile

FROM python:3.11-slim

WORKDIR /app

COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt

COPY . ./

CMD ["python", "app.py"]

This Dockerfile creates a development container for a Python app.

FROM python:3.11-slim sets the base image with Python 3.11.

WORKDIR /app sets the working directory inside the container.

COPY requirements.txt ./ copies the dependencies list.

RUN pip install installs the dependencies.

COPY . ./ copies your app code.

CMD runs the app when the container starts.

Commands

This command builds the Docker image named 'my-python-dev' using the Dockerfile in the current folder. It packages your app and its dependencies.

Terminal

docker build -t my-python-dev .

Expected Output

Sending build context to Docker daemon  4.096kB

Step 1/6 : FROM python:3.11-slim

 ---> 123abc456def

Step 2/6 : WORKDIR /app

 ---> Using cache

 ---> 789ghi012jkl

Step 3/6 : COPY requirements.txt ./

 ---> Using cache

 ---> mno345pqr678

Step 4/6 : RUN pip install --no-cache-dir -r requirements.txt

 ---> Running in abc123def456

Collecting flask

  Downloading Flask-2.3.2-py3-none-any.whl (96 kB)

Installing collected packages: flask

Successfully installed flask-2.3.2

Removing intermediate container abc123def456

 ---> stu901vwx234

Step 5/6 : COPY . ./

 ---> 567yzab890cd

Step 6/6 : CMD ["python", "app.py"]

 ---> Running in efg567hij890

Removing intermediate container efg567hij890

 ---> klm123nop456

Successfully built klm123nop456

Successfully tagged my-python-dev:latest

→

-t - Names and tags the image for easy reference

This command runs the container interactively, removes it after exit, mounts your current folder inside the container for live code changes, and maps port 5000 so you can access the app from your browser.

Terminal

docker run -it --rm -v $(pwd):/app -p 5000:5000 my-python-dev

Expected Output

 * Serving Flask app 'app'

 * Debug mode: off

WARNING: This is a development server. Do not use it in a production deployment.

 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

→

-it - Runs container interactively with a terminal

→

--rm - Removes container after it stops to keep system clean

→

-v - Mounts current directory inside container for live code editing

→

-p - Maps container port to host port for access

This command lists running containers so you can check if your development container is active.

Terminal

docker ps

Expected Output

CONTAINER ID   IMAGE           COMMAND                  CREATED          STATUS          PORTS                    NAMES

klm123nop456   my-python-dev   "python app.py"          10 seconds ago   Up 9 seconds    0.0.0.0:5000->5000/tcp   loving_borg

This command stops the running container named 'loving_borg' to end your development session cleanly.

Terminal

docker stop loving_borg

Expected Output

loving_borg

Key Concept

If you remember nothing else from this pattern, remember: mounting your code folder into the container lets you edit code live without rebuilding the image.

Common Mistakes

Not mounting the code folder with -v, so code changes inside the container are lost after rebuild

Without mounting, the container uses the code copied at build time, so live edits on your computer don't affect the running app

Always use -v $(pwd):/app to mount your current folder inside the container for live development

Not exposing or mapping the app port with -p, so you cannot access the app from your browser

The container runs the app internally, but without port mapping, your computer cannot reach it

Use -p 5000:5000 (or your app port) to map container port to your host

Running the container without --rm, leaving stopped containers cluttering your system

Stopped containers take disk space and make management harder

Use --rm to automatically remove the container after you stop it

Summary

Build a Docker image with your app and dependencies using 'docker build'.

Run the container with code folder mounted and ports mapped for live development.

Use 'docker ps' to check running containers and 'docker stop' to end sessions cleanly.